Electronic pipette systems are utilized to mix precise quantities of various fluids. For example, it may be desired to dilute blood samples or samples of other bodily fluids with a diluent such as saline water before further processing the samples. In order to assure that the results of tests conducted from such diluted samples are accurate, the quantities of both the bodily fluid sample and the diluent must be carefully controlled. These goals may be accomplished in current pipette systems by initially drawing a precise quantity of diluant into the probe. Next a separator air bubble is aspirated, followed by a precise quantity of the fluid sample. The diluent and sample mix when they are dispensed one after the other into an analytical cuvette. Before the next diluent or sample is aspirated into the pipette probe, the probe is washed with a rinse solution. This removes most of the contamination left on the inside and/or outside surfaces of the probe tip from the previous sample.
In order to assure an adequate diluent supply the diluent cup is designed to fill to a precise level. The electronics of the system can detect this level, and thereby confirm that there is adequate diluent supply in the system. If the electronics do not detect liquid at this level, the user is alerted to replenish the diluent supply bottle. Diluent in the cup may all be removed except for the dead volume of the cup which may, for example, be the last 100 micro liters.
One problem with systems of the type described above is that, even with a wash between the taking of a bodily fluid sample and a diluent sample, it is still possible for some of the bodily fluid to adhere to the pipette and to be left behind as a residue in the diluent. This residue may contaminate future samples to be diluted from the same cup and is, therefore, undesirable. However, it is desirable that large quantities of diluent not be required to flush such contaminating residue from the cup between samples.
Apparatus should, therefore, be provided to assure that such contaminants are flushed from the cup containing the diluent or other fluid to be mixed with a bodily fluid sample before a subsequent use so as to avoid contamination. Such apparatus should probably require the use of a minimum quantity of diluent fluid to perform the flush operation.